Speedometer control system and speedometer control method

Abstract

In a speedometer control system having wheel speed sensors as well as a vehicle speed sensor, both a PCM and a brake ECU are used to obtain vehicle speeds. Then, a signal corresponding to a vehicle speed is obtained basically from the PCM. However, if it is impossible to properly obtain a signal corresponding to a vehicle speed from the PCM, a signal corresponding to a vehicle speed is obtained from the brake ECU. Accordingly, even in the event that a signal corresponding to the vehicle speed is not obtained from the PCM, it is possible to obtain a signal corresponding to the vehicle speed from the brake ECU, and thus to display the vehicle speed on a speedometer.

1. A speedometer control system, including: a drive-shaft rotation detection unit for outputting a detection signal corresponding to rotation of a drive shaft connected to driving wheels; a first control portion for outputting a signal corresponding to a vehicle speed based on the detection signal of the drive-shaft rotation detection unit; wheel rotation detection units for outputting detection signals corresponding to the rotations of respective wheels mounted on a vehicle; a second control portion for outputting a signal corresponding to a vehicle speed based on the detection signals of the wheel rotation detection units; a speedometer for displaying vehicle speeds; and a speedometer control portion for receiving the signals corresponding to the vehicle speed from the first control portion and the second control portion, and outputting the signals to the speedometer, characterized in that,
 while the first control portion is outputting the signals corresponding to the vehicle speed in a normal state, the speedometer control portion outputs to the speedometer the signal corresponding to the vehicle speed output from the first control portion, the speedometer displaying the vehicle speed based on the signal corresponding to the vehicle speed output from the first control portion, and that 
 when the first control portion does not output the signal corresponding to the vehicle speed in the normal state, the speedometer control portion outputs to the speedometer the signal corresponding to the vehicle speed output from the second control portion, the speedometer displaying the vehicle speed based on the signal corresponding to the vehicle speed output from the second control portion. 
 
   
   
     2. The speedometer control system according to  claim 1 ,
 wherein the first control portion, the second control portion and the speedometer are connected to each other by means of a communication LAN, characterized in that 
 when the first control portion outputs no signal corresponding to the vehicle speed, the second control portion outputs the signal corresponding to the vehicle speed obtained from the detection signals corresponding to the rotation of the wheels. 
 
   
   
     3. A speedometer control method for displaying a vehicle speed on a speedometer using an output of a signal corresponding to the vehicle speed from a first control portion based on a detection signal from a drive-shaft rotation detection unit which outputs a detection signal corresponding to rotation of a drive shaft connected to driving wheels, the method characterized by comprising:
 outputting a detection signal to a second control portion from wheel rotation detection units that output the detection signal corresponding to rotation of each of wheels mounted on a vehicle; 
 displaying the vehicle speed on the speedometer corresponding to the signal corresponding to the vehicle speed output from the first control portion when the first control portion outputs the signal corresponding to the vehicle speed in a normal state; and 
 displaying a vehicle speed on the speedometer by outputting to the speedometer from the second control portion a signal corresponding to the vehicle speed obtained from the detection signal corresponding to the rotation of each of the wheels by the second control portion, when the first control portion does not output the signal corresponding to the vehicle speed in the normal state.